4f15267d3d
This change is almost fully mechanical. The only interesting change is in `generate_feature_test_macro_components.py` to generate `_LIBCPP_STD_VER >=` instead. To avoid churn in the git-blame this commit should be added to the `.git-blame-ignore-revs` once committed. Reviewed By: ldionne, var-const, #libc Spies: jloser, libcxx-commits, arichardson, arphaman, wenlei Differential Revision: https://reviews.llvm.org/D143962
115 lines
3.7 KiB
C++
115 lines
3.7 KiB
C++
// -*- C++ -*-
|
|
//===----------------------------------------------------------------------===//
|
|
//
|
|
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
|
|
// See https://llvm.org/LICENSE.txt for license information.
|
|
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
#ifndef _LIBCPP___RANGES_NON_PROPAGATING_CACHE_H
|
|
#define _LIBCPP___RANGES_NON_PROPAGATING_CACHE_H
|
|
|
|
#include <__config>
|
|
#include <__iterator/concepts.h> // indirectly_readable
|
|
#include <__iterator/iterator_traits.h> // iter_reference_t
|
|
#include <__memory/addressof.h>
|
|
#include <__utility/forward.h>
|
|
#include <optional>
|
|
#include <type_traits>
|
|
|
|
#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
|
|
# pragma GCC system_header
|
|
#endif
|
|
|
|
_LIBCPP_BEGIN_NAMESPACE_STD
|
|
|
|
#if _LIBCPP_STD_VER >= 20
|
|
|
|
namespace ranges {
|
|
// __non_propagating_cache is a helper type that allows storing an optional value in it,
|
|
// but which does not copy the source's value when it is copy constructed/assigned to,
|
|
// and which resets the source's value when it is moved-from.
|
|
//
|
|
// This type is used as an implementation detail of some views that need to cache the
|
|
// result of `begin()` in order to provide an amortized O(1) begin() method. Typically,
|
|
// we don't want to propagate the value of the cache upon copy because the cached iterator
|
|
// may refer to internal details of the source view.
|
|
template<class _Tp>
|
|
requires is_object_v<_Tp>
|
|
class _LIBCPP_TEMPLATE_VIS __non_propagating_cache {
|
|
struct __from_tag { };
|
|
struct __forward_tag { };
|
|
|
|
// This helper class is needed to perform copy and move elision when
|
|
// constructing the contained type from an iterator.
|
|
struct __wrapper {
|
|
template<class ..._Args>
|
|
constexpr explicit __wrapper(__forward_tag, _Args&& ...__args) : __t_(std::forward<_Args>(__args)...) { }
|
|
template<class _Fn>
|
|
constexpr explicit __wrapper(__from_tag, _Fn const& __f) : __t_(__f()) { }
|
|
_Tp __t_;
|
|
};
|
|
|
|
optional<__wrapper> __value_ = nullopt;
|
|
|
|
public:
|
|
_LIBCPP_HIDE_FROM_ABI __non_propagating_cache() = default;
|
|
|
|
_LIBCPP_HIDE_FROM_ABI
|
|
constexpr __non_propagating_cache(__non_propagating_cache const&) noexcept
|
|
: __value_(nullopt)
|
|
{ }
|
|
|
|
_LIBCPP_HIDE_FROM_ABI
|
|
constexpr __non_propagating_cache(__non_propagating_cache&& __other) noexcept
|
|
: __value_(nullopt)
|
|
{
|
|
__other.__value_.reset();
|
|
}
|
|
|
|
_LIBCPP_HIDE_FROM_ABI
|
|
constexpr __non_propagating_cache& operator=(__non_propagating_cache const& __other) noexcept {
|
|
if (this != std::addressof(__other)) {
|
|
__value_.reset();
|
|
}
|
|
return *this;
|
|
}
|
|
|
|
_LIBCPP_HIDE_FROM_ABI
|
|
constexpr __non_propagating_cache& operator=(__non_propagating_cache&& __other) noexcept {
|
|
__value_.reset();
|
|
__other.__value_.reset();
|
|
return *this;
|
|
}
|
|
|
|
_LIBCPP_HIDE_FROM_ABI
|
|
constexpr _Tp& operator*() { return __value_->__t_; }
|
|
_LIBCPP_HIDE_FROM_ABI
|
|
constexpr _Tp const& operator*() const { return __value_->__t_; }
|
|
|
|
_LIBCPP_HIDE_FROM_ABI
|
|
constexpr bool __has_value() const { return __value_.has_value(); }
|
|
|
|
template<class _Fn>
|
|
_LIBCPP_HIDE_FROM_ABI
|
|
constexpr _Tp& __emplace_from(_Fn const& __f) {
|
|
return __value_.emplace(__from_tag{}, __f).__t_;
|
|
}
|
|
|
|
template<class ..._Args>
|
|
_LIBCPP_HIDE_FROM_ABI
|
|
constexpr _Tp& __emplace(_Args&& ...__args) {
|
|
return __value_.emplace(__forward_tag{}, std::forward<_Args>(__args)...).__t_;
|
|
}
|
|
};
|
|
|
|
struct __empty_cache { };
|
|
} // namespace ranges
|
|
|
|
#endif // _LIBCPP_STD_VER >= 20
|
|
|
|
_LIBCPP_END_NAMESPACE_STD
|
|
|
|
#endif // _LIBCPP___RANGES_NON_PROPAGATING_CACHE_H
|